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Traffc Calming:
County Report January 2000


      (703) 228-3681

      January 18, 2000

      Dear Advisory Group Member:

      I am pleased to enclose a copy of the report describing the proposed Neighborhood Traffic Calming Program for your review and comment. This report represents the work of the Neighborhood Traffic Calming Committee (NTCC) that was appointed last year by the County Board to develop a process and criteria for implementing traffic calming measures that can be considered to address traffic problems on neighborhoods streets. The report will be considered by the County Board on March 11, 2000.

      The advisory group on which you serve will consider this item in the near future, and I want to provide plenty of time for your review of the report. The dates for consideration of this report by the various advisory groups are indicated below:

        Planning Commission on January 31 at the 7:00 p.m. 'pre-meeting"

        Arlington County Civic Federation on February 1

        Neighborhood Conservation Advisory Committee (NCAC) on February 10

        Transportation Commission on February 16.

      Should you have questions about the report, please feel free to call Jeff Sikes, NTCC staff coordinator, at (703) 228-3696. Thank you for cooperation and interest in this important program to make Arlington's neighborhood streets safer and more livable


      Charles Denney

      Arlington County, Virginia

      Neighborhood Traffic Calming Committee

      Report on Arlington County s Neighborhood Traffic Calming Program Process Criteria and Measures

      January 19, 2000




      On March 13, 1999, the Arlington County Board appointed a committee to develop policies and procedures for a program as set forth by the Ad Hoc Committee on Neighborhood Traffic Calming (NTC) in November of 1998. The document that follows reflects the work of this Neighborhood Traffic Calming Committee (NTCC). It is comprised of the following Chapters:

        I. Mission Statement, Goals, Objectives, and Strategies
        II. Problem-Solving Process:

          * Identify Problem
          * Define Scope of Problem
          * Collect Data to Confirm Existence of Problem
          * Community Discussion of Confirmed Problems and NTC Measures
          * Development of Action Plan
          * Assessment of Community Support for Action Plan
          * Project Funding
          * Project Implementation
          * Follow-up Evaluation of NTC Project
          * Program Review and Refinement
        III. Traffic Calming Measures and Criteria
          * Traffic Calming Toolbox


        i. NTC Process Flow Chart
        ii. Project Ranking Guidelines
        iii. NTCC Funding Schedule
        iv. Citizen Appeals
        v. 85th Percentile Speed

      In general, the Committee based its work on the Final Report of the Ad Hoc Committee. We diverged, however, in our approach to solving problems. Whereas, the Ad Hoc Committee's report was oriented around specific traffic calming measures, the NTC Committee developed a "problem-oriented" procedure aimed at finding the most appropriate measures for each situation.

      Our philosophy was to use standard measurements to determine the severity of traffic problems. This information would then suggest a range of traffic calming measures as well as the level of public involvement required to develop an action plan.

      The community would be supported and assisted by the NTCC and the Planning Division of the Department of Public Works in their efforts to solve their documented traffic problems.

      Finally, we built into the new process tools to evaluate the success of each project and the process in general. For each completed project, follow-up data will be collected to determine the effectiveness of the traffic calming measures installed. At periodic intervals, these data will be evaluated as well as other information provided by citizens affected by our work to identify any needed changes to the program, standard traffic measurements, criteria for each traffic calming measure, or the process in general.


      Chapter I: Mission Statement, Goals, Objectives, and Strategies

      Chapter II: Problem Solving Process

        Identify Problem

        Define Scope of Problem

        Collect Data to Confirm Existence of Problem

        Community Discussion of Confirmed Problems and NTC Measures

        Development of Action Plan

        Assessment of Community Support for Action Man

        Project Funding

        Project Implementation

        Follow-up Evaluation of NTC Project

        Program Review and Refinement

      Chapter III: Traffic Calming

        Traffic Calming Toolbox


        Neighborhood Traffic Calming Process Flow

        Project Ranking Guidelines

        NTCC Funding Schedule

        Citizen Appeals

        85th Percentile Speed



      Develop and oversee a program to support the County Board's vision of an "urban village" by reducing the impact of vehicular traffic and improving pedestrian and bicyclist safety within and around residential areas in Arlington County.


      1. Change the culture of neighborhood street use from "cars first" to "people first."

      2. Develop street design guidelines which will make speed limits and other traffic controls on residential minor and principal streets "self-enforcing."

      3. Coordinate NTCC efforts with the Pedestrian, Bicyclist, and ADA advisory committees.

      4. Establish effective, fair, and consistent policies for implementing traffic calming measures.

      5. Ensure that neighborhood street use is consistent with Master Transportation Plan designations and zoning to the greatest extent possible.

      6. Redirect through traffic to the arterial road network.

      7. Foster collaboration and a shared sense of purpose between County residents and staff in addressing traffic problems.

      8. Reduce the number of cases requiring County Board intervention.


      Note: numbering as in original report.
      9. Refine County policies governing the NTC program and application of traffic calming measures.

      10. Develop the NTC Program.

      11. Implement the NTC Program.

      12. Evaluate and refine the NTC Program

      13. Make final recommendations to the County Board.


      1. Refine County Policies governing the NTC Program and application of traffic calming measures.

      a) Establish maximum tolerable speed and volume standards for residential streets.

      b) Develop a formula incorporating number of residences, traffic volume, speed to determine extent to which streets are out of compliance.

      c) Establish requirements for community outreach for each traffic calming measure

      d) Develop criteria for applying traffic calming measures to problem streets.

      e) Develop priorities for scheduling traffic calming projects.

        Severity of problem Scope
        Order in which received
        Budget considerations
        Community Support

      f) Review County policies and public statements

      g) Issues:

        Do Master Transportation Plan street classifications match actual use?

        What is the County's objective for streets which are classified as neighborhood streets but carry through traffic?

        How far should the County go to move through traffic to the arterial roads?

        How do we balance the interests of residents and users?


      a) Identify and refine data collection tools, methods, and procedures, including:

        Origin-destination surveys
        Speed classifiers
        Review of street characteristics
        Review of street use
        Comparison of expected vs. actual street use
        Resident surveys before, during, and after traffic calming measure installation

      b) Develop communications tools to support and increase the effectiveness of the program, including:

        Resource manual for citizens explaining policies and procedures
        Public information campaign
        Web site
        Public Meetings
        ~ Consensus-building sessions

      c) Design procedure for notifying interested parties

      d) Define traffic calming elements which prioritize pedestrian, bicyclist, and wheelchair safety.

        Street width
        crossing distances
        bicycle paths
        street geometry ~ wheelchair ramps
        pedestrian amenities (sidewalk and tree lawn width, islands, etc.)


        Analysis and Design:

          a) Evaluate and prioritize new NTC project requests
          b) Assign staff and NTCC Members to new projects
          c) Perform community outreach to reach neighborhood consensus about problems
          d) Identify traffic calming measures to address problems
          e) Review and refine proposals with community
          f) Identify issues requiring resolution by the NTCC or County Board.
          g) Determine resource requirements
          h) Prepare budget for new projects
          i) Submit new project request to the NTCC for approval


          j) Prioritize existing (approved and funded) NTC projects
          k) Develop work plan and schedule
          1) Evaluate newly approved NTC projects
          m) Obtain resources
          n) Prioritize new NTC projects
          o) Monitor construction


        a) Collect follow-up data (speed, volume, pedestrian safety, resident satisfaction, etc.)
        b) Analyze results of NTC projects
        c) Recommend corrective program action
        d) Research new traffic calming strategies (on-going)
        e) Revise resource requirements
        f) Revise work plan and schedule
        g) Report periodically to the County Board

      5. Make final recommendations to the county Board

        a) Compile results of data collected on completed projects to show overall results of NTC program
        b) Recommend policy changes
        c) Identify policy issues needing Board resolution.



      Neighborhood traffic problems are addressed through several steps. First, residents' perceptions of problems and their goals must be defined. Second, the specific traffic problem needs to be defined and quantified. Third, if there is a discrepancy between perceptions and data, this difference must be evaluated. Forth, the most appropriate traffic calming measure(s) must be selected. Fifth, the affected residents must agree on the proposed traffic calming measures. And sixth, the project must be funded

      The process described below represents a community-based, "problemoriented" approach to deciding what to do about neighborhood traffic problems. The emphasis is on selecting traffic calming measures which will address documented problems instead of allowing preconceived, unstudied proposals to drive the process.

      Underlying this new process are standards and criteria which determine the existence and severity of traffic problems. These standards and criteria are based on those used in successful traffic calming programs in North America and Europe. The criteria used herein correspond to requirements for individual traffic calming measures. In other words, traffic problems severe enough to warrant action would qualify for one or more of the approved traffic calming measures available for use in Arlington County.

      Regardless of the scope of the traffic situation, the problem-oriented process is the same. The difference is in how broad the community participation must be. For example, addressing a speeding problem on a single block of a street would not require the same level of public discourse as a problem affecting several streets within a neighborhood. The most difficult problems are those where road users and affected residents have conflicting but equally valid needs. Central to the new process is an acknowledgment that communities need outside support to identify and solve traffic problems while respecting the interests of all affected parties.


      The Neighborhood Traffic Calming Committee oversees the problem-solving process. When requests for traffic calming come in, from whatever source, Staff determine what course of action to follow. In some cases, Staff may propose to implement one of several regularly budgeted traffic control measures not subject to the

      Traffic calming measures included in neighborhood action plans should be appropriate for the problem(s) being solved, result from the community working group considering all relevant viewpoints and opinions and should meet with community approval.

      If the affected community approves the action plan, then the plan becomes eligible for funding. Like the Neighborhood Conservation Advisory Committee (NCAC) funding process, NTC projects will be funded in six-month cycles. Funded projects will be scheduled for implementation. Unfunded projects will be referred back to staff who will send the requesters a letter informing them of their options.

      After an NTC project has been implemented and in place for several months, Staff and the NTCC will conduct a follow-up evaluation to determine the success of the project in solving the identified problem. The results of this evaluation will determine whether the NTCC needs to revisit the problem. Additionally, the results will be used during periodic programmatic reviews of the standards and criteria which form the basis of this program and to assess the effectiveness of specific traffic calming measures.



        Requests for traffic controls can come from an individual citizen, groups of citizens, civic associations, businesses, developers, County staff, or the County Board. It is important for the requester to focus on the problem and not let a preconceived, unstudied solution drive the process


        Staff can initiate the NTC process when seeking to correct situations which are brought to their attention. For these problems, staff should recommend corrections to the NTCC. The NTCC will determine the appropriate level of public participation.

        Upon receipt of a request for NTCC assistance, Staff will forward a questionnaire to the requester to gather the following information:

        • Name(s) of Requester(s), contact information, and length of time in residence
        • Description of the problem
        • Specific location(s) of traffic problem(s)
        • Time of day when problem occurs
        • Dates/times of accidents (reportable and non-reportable)
        • When the problem started
        • Possible causes of the problem? (opinion)
        • Any perceived dangers to pedestrians, residents, property as a result of the problem (opinion)
        • Results residents hope to achieve (i.e., reduced speed, lower traffic volume, fewer accidents, lower risks to pedestrians, etc.)
        • Names, addresses, phone numbers of nearby residents who share the concerns

        Staff will acknowledge the completed questionnaire in writing to those whose names were provided and to the civic association (if any) and the NCAC representative (if any). This communication will outline the next steps to be taken and provide a time frame for collecting data and assessing the problem.


      Using the completed questionnaire, staff will inspect the area and review other information such as road and land-use maps to identify technical issues and to clarify their understanding of the problem from the requester's perspective. Specifically, staff will:

        Identify affected streets and intersections
        Identify users of affected streets and intersections (stakeholders)
        Identify traffic generators
        Analyze street use with respect to street classification
        Document any other factors which might contribute the problem

      Once staff understands the scope of the problem in terms of geography and road use, its next step is to collect data which will determine whether the problem meets any of the thresholds set by the NTCC and approved by the County Board.

      Depending on the type of problem to be analyzed, some or all of the following data will be collected :

      (Footnote: Appendix should describe specifications for each data collection effort)

        Traffic Counts
        Speeding Studies (classifier, police radar, etc.)
        Origin/Destination Studies
        Resident Opinion Surveys
        Field observations
        Other, to be identified as needed

      Staff will review the results of the data collected and compare with the established criteria for identifying traffic problems. They will also add the location to the County's NTC Problem Database for reference and NTC Program review.


      If the data collected indicate that the situation does not meet the thresholds which define traffic problems, staff will send a report to the NTCC with the results of the data and recommend that no action be taken. The situation will be eligible for reevaluation after a two-year waiting period.

      Staff will report back to the community that the problem did not warrant any specific action by the NTCC or staff. If this response is not satisfactory, the citizens may request that the NTCC put the issue on its agenda for a brief presentation by the proponents in a future meeting. Additionally, as part of the on-going programmatic review of the NTC and the appeals processes, all problems for which measures have not been implemented by NTCC may be reviewed at a later time to determine whether the NTC thresholds and criteria are too narrow or the process breaks down in certain areas.


      If the objective data confirm the existence of a problem (which may or may not be the same problem identified by the requester), staff will prepare a problem report including:

        Date request for help received
        Name(s) of requester(s) and contact information
        Problem Inventory (specific locations, times or day, etc.)
        Dates/times of accidents (reportable and non-reportable)
        Traffic Data Analysis (details attached)
        Causes of problems
        Risks to pedestrians, residents, property as a result of the problem
        Geographic scope and boundaries
        Potential Solutions
        Names, addresses, phone numbers of nearby residents who share the concerns
        List of people willing to work with the NTCC to solve problems
        Date and time for meeting to discuss potential solutions and community role (if applicable)

      Staff will forward this problem report to the NTCC for information and to the original requester, the civic association (if any), and the NCAC representative (if any), and any other individuals who have made their interest known by letter or petition. The NTCC will assign a member to oversee the community outreach and consensus-building required to decide how best to address the problem.


      The NTCC representative and staff will meet with the original requesters to discuss possible courses of action. The initial meeting will have the following purposes:

        Educate citizens about the process
        Review the collected data
        Discuss applicable NTC measures and requirements for each
        Review process for achieving consensus on NTC measures
        Formation of a working group

      At this early stage, the discussion will focus on the problems rather than the merits of specific traffic control measures. Participants should leave these sessions understanding:

        The scope and nature of the problems in their community
        The NTC process that will be followed
        What they can realistically expect from traffic calming
        The necessity for working within their community to build a consensus for NTC measures

      Staff, the NTCC representative, and facilitator (if any) should leave the meeting with an understanding of:

        What residents hope to achieve
        Sources of potential conflict within the neighborhood
        Any issues not previously identified
        A sense of the extent of community support for the NTCC effort to solve the problem(s)


      The number of working group meetings will depend on the complexity of the problem or problems. For complex problems, the NTCC will allow the community a period of three months to form a working group of the affected residents and other interested parties. If no working group has formed, the NTCC will consider whether to grant an extension or conclude the project.

      The working group will be requested to produce periodic status reports to the NTCC for longer-term projects. If it appears that a community cannot reach agreement on an action plan, the NTCC may recommend that the community effort be suspended.

      The outcome of the community problem-solving process should be a proposed plan of action. This can be as simple as a single traffic calming measure or as complicated as a neighborhood-wide plan.


      When the working group has developed an action plan, Staff, the NTCC representative, and the working group representative will present it to the NTCC for discussion and comments.


      Each proposed traffic calming measure within the action plan requires a certain level of community support to be eligible for funding and implementation. To assess community support, Staff will prepare the following materials to mail to the affected households:

        Letter explaining the proposed action plan and announcing a community meeting
        Maps and diagrams explaining what the proposed measures will look like and where each will be located.
        Level of response and support required for NTCC approval of plan.
        Postage-paid return card with the resident's name, address, required signature line, and a "yes" or "no" box to be checked, as well as space for comments.

      If an insufficient number of households respond within four weeks, members of the community working group assigned to that particular project will follow-up with those neighbors who failed to return their cards.

      Support of the civic association(s) and local PTA's is not required but is strongly encouraged.

      If the response is sufficient but negative toward the proposal, the NTCC will recommend either that the problem be referred back to the community outreach phase or that it be closed out as irreconcilable. If the project is referred back to the community, the NTCC may recommend alternative approaches, more likely to meet with community acceptance.

      In the case of projects failing to receive support and being closed out, the NTCC will determine a minimum waiting period - one to four years - before the problem or problems may be resubmitted for NTCC assistance." Footnote: See Appendix 4: Citizen Appeals for more information



      In order to avoid diverting traffic from one neighborhood street to another, the NTCC supports the analysis of traffic problems on a neighborhood-wide basis and the development of a comprehensive plan to calm traffic throughout a neighborhood. This is similar to the process undertaken during development of a Neighborhood Conservation Plan under the NC program.

      However, when it comes time to provide funds for the implementation of specific traffic calming measures, the NTCC will evaluate projects on a street-by-street basis, through the use of a priority ranking system (see Appendix 1). The system is intended to provide the NTCC with an objective method for assessing the severity of the traffic calming issue the project is intended to address. Other things being equal, projects with more severe problems, as shown by higher point values, will be recommended for funding before projects with less severe problems, as shown by their lower point values.

      Prior to full NTCC discussion, its rankings subcommittee, working with County staff, will assign points to each eligible project under the NTCC project priority ranking guidelines subject to review by the full NTCC.

      The proposed ranking system gives equal stress to speeding and volume, and assigns points for every reported, traffic calming- related accident. Additional points are given to projects on streets used by bicyclists and transit riders, with facilities that generate substantial amounts of pedestrian traffic, and with conditions leading to increased hazards. Further preference is given to projects that demonstrate high levels of community support.


      NTCC will place all eligible projects on a list for consideration during twice yearly NTCC funding sessions (see Appendix 2). Eligible projects will be discussed at the NTCC meeting prior to each funding session, and NTCC members are expected to visit eligible sites prior to the funding session. The funding process will proceed in the following fashion:

        1. For each project, in priority order as determined by the point system:

        • County staff describes project;
        • Supporters and opponents of project are provided the opportunity to speak for or against funding; and
        • NTCC members discuss specific issues.

        2. NTCC debates and recommends project funding Recommended projects funded through bond issues will be referred to the County Board for final approval; projects recommended for funding through operational accounts will be referred to the County Manager.

        Projects not recommended for NTC funding, for whatever reason, may be eligible for other funding sources, such as the Neighborhood Conservation Program and will be referred back to the community to investigate other funding sources. They also may remain on the NTC eligible projects list for subsequent funding sessions.


      Once a project has been approved and funded, Staff performs the following actions:

      • Preliminary engineering to determine scope of work
      • Perform site survey
      • Develop detailed construction drawings
      • Acquire rights of way and easements
      • Schedule construction either by County Staff or contractor
      • Notify affected residents of construction schedule
      • Execute construction
      • Install landscaping treatments
      • Repair any damage to private property


      a) Staff Collects "After" Data

      • Repeat Tests from Initial Data Collection
      • Perform Other Tests as Needed
      • Survey residents
      • Track changes in traffic patterns

      b) NTCC and Staff Prepare Evaluation Report

      • Compare "Before" and "After" Data
      • Analyze Results
      • Identify Next Steps and/or Corrective Actions for Failures

      c) Close Out Problem

      • Prepare Item for inclusion in periodic County Board Report
      • Remove Project from Schedule
      • Communicate with Citizens on any remaining issues, problems, or concerns


      Periodically, the NTCC will review the approved standards and criteria to determine whether they are appropriate for current conditions. This analysis will consider all NTC requests which did not meet the thresholds as well as those which did. Additionally, citizens who feel that the NTC Process needs refinement may bring their issues to the table for discussion and consideration by the NTCC and the County Board liaison.

      It is important that Arlington County citizens find the NTC process to be fair and the policies consistently applied. Additionally, because this is a new program, the NTCC will closely monitor the following areas for effectiveness:

      • The criteria used to determine whether a problem exists and how severe it is;
      • The criteria which must be met in order to qualify for a traffic calming measure;
      • The funding priorities
      • The process
      • Budget requirements

      The initial review will take place one year after the County Board approves the NTC Program.


      Traffic calming involves implementing strategic measures to reduce vehicle speed, excessive traffic volume, cut-through traffic on residential streets, and other safety-related neighborhood traffic concerns. The following definitions, measures and criteria are established for the NTC process.


      A. Speeding

      A speeding problem exists when the 85th percentile speed on the affected street/s is in excess of 5 mph over the posted speed limit for at least a period of 24 hours or another appropriate time period determined by Staff. In other words, more than 15 percent of the drivers on the street travel more than 5 mph over the posted speed limit. This problem may exist over the course of the entire day. Other speeding-related problems may exist, such as infrequent high speed vehicles. Efforts to address these speeding problems can also be undertaken.

      B. Excessive Traffic Volume

      Excessive traffic volume is a disproportionately high volume of traffic that seems to promote excessive speeds, unsafe driving behaviors, and diminished livability on a neighborhood street s. Defined on a case-by-case basis.

      C. Excessive Cut-through Traffic An excessive cut-through problem exists when more than 30% of the traffic in any given hour during the day uses the street/streets as a through street. Cut through traffic is defined as traffic not originating in or destined to the immediate neighborhood.

      D. Other Neighborhood Traffic-Related Issues

      Other traffic-related issues include lack of convenient crosswalks, lack of sidewalks, hazards for bicyclists, excessive noise from vehicles/trucks, etc. Safety for pedestrians may be an issue near schools, elderly living centers, playgrounds and other pedestrian traffic generators.


      The following is a list of measures available for use in traffic calming: nubs, traffic circles, street narrowing, raised crosswalk, median (raised or flush), chicane, rumble strips, flat top speed humps (not bumps), street closure (full and half), turn/ access restrictions, diverters (diagonal and semi), gateway treatments. woonerf, raised crosswalk, and truck restrictions.

      Some measures are available for implementation under authority of the County Manager and do not need to go through the full NTC process such as roadway markings, mid-block crosswalks, multi-way stop signs, $200 warning signs for speeding, placement of a speed display trailer, arterial direction signs, marking of bike lanes, changes in parking restrictions, vegetation trimming, additional speed limit signs or "Stop Ahead" signs, and education programs. Measures are further addressed in the table in section 4.

      The following is a list of considerations when selecting a measure for traffic calming. The measure selected, in general, should be:

      • the most effective available
      • the least adverse in impact
      • the simplest available
      • the least costly possible
      • a stand-alone or single measure or in combination with other(s)
      • within the range of professional traffic management guidelines
      • a contribution to the overall attractiveness of County streets


      The following factors should be considered when selecting a traffic calming measure.

        A. Community Support: Speeding solutions should be supported by 60% of the households of the affected street/s. Cut-through solutions should receive 60% support from the households in the affected area, where the area includes not just the affected street but other potential parallel cut through streets, and or the entire neighborhood area bounded by the arterials which are generating the cut-though traffic. Some specific examples: Traffic Circles should obtain 60% support from the households on the affected streets within one block of the circle. Nubs should obtain support from 60% of the households on the affected street within one block of the intersection. See table for additional specifics.

        B. Traffic Volume: Streets with defined traffic problems, but lower volumes of traffic may receive lower priority, less restrictive measures, and/or less expensive measures.

        C. Effectiveness: Can the measure solve the problem, based on past experience here and elsewhere.

        D. Street Geometrics: Street width, intersection size, and topography may lead to the exclusion or selection of certain measures. For example an overly small intersection may not be sufficiently large to accommodate a traffic circle.

        E.Community Preference: A community will not be forced to receive a measure it does not support, and must show significant support (60%) for the measures it does want.

        F. Existence of transit route, major school bus route or Emergency Medical Service Route: Additional approval and evaluation may be needed depending on the measure desired.

        G. Schools: The presence of schools near a location increases the need for controlled vehicular traffic. However, vehicle trips for pick-up and drop-off to a school located in the neighborhood is not considered cut- through traffic, and should not be counted as such in a DPW analysis of the traffic data.

        H. Community/Organization Support: The views of the local civic association/s or local PTA/s will be considered.

        I. Traffic Management Resources: The Manual on Uniform Traffic Control Devices and other relevant professional traffic management publications may provide guidance on the selection of measures.


                                   Support       Relative
  Used for	Measure     Criteria   Needed	     Cost	    Comments

1 Convenience, Roadway MUTCD none low safety Markings* information 2 Cut-through Street Cut- 60% of high traffic Closure through households traffic in the problem designated area of impact** 3 Cut-through Diverters Cut- 60% of high traffic through households traffic in the problem designated area of impact** 4 Cut-through Half Cut- 60% of high traffic Street through households Closure traffic in the problem designated area of impact** 5 Cut-through Turn & Cut- 60% of low Cut-through traffic Access through households problem at Restric- traffic in the certain tions problem designated times of area of the day impact** 6 Cut-through One-Way Cut- 60% of low traffic Streets through households traffic in the problem designated area of impact** 7 Cut-through Truck Requires Approval low traffic Restric- County of Civic tions Board Assn. Approval 8 Cut-through Woonerf To be To be high traffic, determined determined speeding 9 Inter- Multi- See Approval low High section Way revised of Civic expectation safety, Stop warrants Assn. on non- pedest. Sign adopted compliance safety by the if vpd is County not high Board on 10/7/99 10 Pedest. Midblock signifi- 60% of low safety cross- cant households walk * concentra- in the tion of designated pedest. area of traffic impact** 11 Speeding Traffic -85th% > 60% of high Not for 3-way Circle 30 mph. households or offset -only with within intersections consent of one block Fire Dept. of circle & Transit assoc. -major street to have low left turn volume 12 Speeding Narrow 85th% > 60% of high Usually done streets 5 mph households where no curb above the in blocks & gutter in speed to be limit narrowed 13 Speeding Slow 85th% > 60% of high May impact Points 30 mph households on-street in block parking to be installed 14 Speeding Median 85th% > 60% of high Affects 30 mph households driveway in the access to designated residences area of high impact 15 Speeding Chicane To be To be high determined determined 16 Speeding $200 Fine Used where Approval low Speed chronic of Civic Warning excessive Assn. Signs speeding 17 Speeding Median Where 60% of low May be Bollards speed households used to (SPCCD) limit < in block(s) enhance 30 mph where pedest. -85th% > installed safety. 30 mph. Messages -not on on signs roads w/ may > 1 lane change. in each direction -requires painted or raised median. 18 Speeding Flat-top -85th% > 60% of medium Area Speed Hump 32 mph households petitioned -only with on street may need to consent of to be adjusted Fire Dept. receive based on & Transit humps street assoc. network -street grades < 8% 19 Warning Rumble -85th% > 60% of medium May cause Strips 30mph households noise in block complaints. to be Dangerous installed for medium -Dangerous for bicyclists. 20 Speeding Speed any as none Display citizen requested Trailer * complaint 21 Speeding, Gateway -85th% > 60% of high -Affected cut- 30 mph households area to be in affected determined area on a case by case basis -May discourage cut-through 22 Speeding, Nubs -85th% > 60% of high Also Pedest. (curb 30 mph households pedestrian safety extensions, within benefits chokers) one block 23 Speeding, Raised -85th% > 60% of medium pedest. Crosswalk 32 mph households safety -Only w/ on street consent where of Fire installed Dept & Transit Assoc. -major ped crossing point 24 Traffic Arterial MUTCD Approval low Volume Direction of Civic Reduction Signs Assn. * Administrative measures can be implemented by staff without going through the NTC process ** Areas of impact for these measures are to be determined on a case-by-case basis Notes: All measures can be used on neighborhood minor and principal streets, but measures 1,9,10,20,24 can also be used on arterials and 12,17,22 can be used on minor arterials


      Project Ranking Guidelines

      Measures and Definitions


        Average daily percentage of vehicles traveling more than 5 mph over the speed limit, at the point on the project street with the highest average speed. Points: 0-30


        Average daily traffic volume, at the point on the project street with the highest average volume, divided by 100. Points: 0-30


        Number of reported, correctable accidents on the project street in the last three years. Points: 5 each

      Bike/Transit Routes

        Street designated as Official or Unofficial Bicycle Route on the Arlington County Bikeways Map, or used as a regular transit route by Metro Bus. Points: 5 each

      Pedestrian Generators

        Public and private facilities on or near the project street, such as schools, parks, community houses, senior housing, etc., which generate a substantial amount of pedestrian traffic. Points: 5 each

      Dangerous Conditions

        Conditions on the project street which lead to increased hazards, such as the absence of a sidewalk on either side of the street or inadequate, uncorrectable site distance problems. Points: 5 each

      Community Support

        Support from civic association or local PTA; each ten percentage points above required 60% on qualifying petitions/cards. Points: 5 each


      February 15
      Deadline for project qualification and consideration by citizens' association

      Eligible projects discussed at NTCC meeting

      Project funding session

      August 15
      Deadline for project qualification and consideration by citizens' association

      Eligible projects discussed at NTCC meeting

      Project funding session

      Note: Neighborhood Conservation Advisory Committee funding sessions are held in June and December, thus giving applicants additional opportunities to obtain support for their projects.


      One of the NTCC's stated goals is to establish effective, fair, and consistent policies for implementing traffic calming measures. To that end, the most severe traffic problems will receive the highest priority for funding and implementation. Underlying the NTC Program are standard measures which define the severity of traffic problems. Often residents perceive that a problem exists when in fact one does not. Many traffic problems are not severe enough to qualify for NTCC assistance. Standard data collection tools and procedures will ensure that all problems are assessed in a consistent manner.

      For confirmed traffic problems, each NTC measure has certain criteria which must be met. What this means is that even when a traffic problem has been documented, there may not be enough support within the neighborhood for the proposed traffic calming measures.

      NTC Projects for which all criteria have been met and are eligible for funding may not receive funding because of higher priority projects and limited funds.

      There may be citizens who feel that their traffic situation has not received a fair hearing by the NTCC and wish to appeal on that basis.

      During the first year of operation, the NTCC will study the application of the measures and criteria to determine whether they are too broadly or narrowly drawn. In other words, criteria should be narrow enough that not every street in Arlington would qualify for traffic calming, but broad enough that traffic calming measures will be installed where the greatest need exists.

      Citizens whose traffic problems were not found to be severe enough to qualify for traffic calming may request a meeting with the NTCC to discuss the data collected and the criteria the data were measured against. For situations where a problem was documented but the community could not agree on what to do about it, the community may resubmit their request in one to four years at the NTCC's option depending on the scope and complexity of the problem to be addressed. Specifically, a problem which is narrow in scope and simple to address could be revisited in one year. On the other hand, a larger scale community effort which requires extensive staff and NTCC resources may not be reconsidered by the NTCC for at least four years. The NTCC will make the determination as to an appropriate waiting period on a case by case basis at regularly scheduled meetings.

      In cases where a project was approved for funding but no NTC funds were available, the NTCC and Public Works Planning staff will inform residents of their options.

      Finally, citizens are invited to participate in the periodic programmatic review meetings and share their thoughts about how the NTC program could be improved.


      Definition: "That speed below which 85 percent of all traffic units travel, and above which 15 percent travel."
      Footnote: Traffic Engineering- Theory and Practice, Louis J. Pignotara

      What is the 85'h percentile speed and why do we use it?

      In general, it is an accepted principle that the majority of drivers on a roadway select safe and proper speeds based on roadway and traffic conditions. For determining a speeding problem on a specific roadway, the 85'h percentile speed is often used because it is usually seen as approximately the high end of the "normal´┐Ż speeds traveled by motorists on a given roadway. To illustrate the 85th percentile speed statistic, the attached figure was prepared, which shows a bell curve that was created by arranging all of the recorded vehicle speeds from a study in order from the lowest to the highest. In general, the 85th percentile speed statistic is of particular interest because it is often located at about the upper end of the speed range which includes a good majority of the traffic which is considered to select "safe and proper speeds." (See figure.) Typically, recorded speeds along the bell curve above the 85th percentile speed tend to occur much less frequently than the speeds below it. This is usually because the highest speeds recorded in a study are often erroneous readings or can be the result of a few motorists who are very unperceptive of roadway conditions or irresponsible.

      How does the 85th percentile speed relate to Speed Limits?

      The generally accepted traffic engineering practice is that speed limits should be set at the nearest 5 mph increment to the 85" percentile speed. For instance, if the 85th percentile speed on a road is measured to be 27 mph, then the speed limit on the road would typically be set at 25 mph. However, other considerations such as accidents and real dangers not perceivable by drivers may indicate the need for a lower speed limit. Since speed limits are generally set using the 85'h percentile, it is expected that 15 percent of the vehicles will exceed the speed limit on a regular basis.

      How does the 85th percentile speed relate to speeding problems?

      Frequently, a County engineering study will show that the 85'h percentile speed exceeds the speed limit of 25 mph established by the State code. Currently, if the 85'h percentile speed falls within the range of 25-30, it is not considered a speeding problem in Arlington County since this is reasonably close to the speed limit on neighborhood streets. Once the 85th percentile speed exceeds 30 mph, however, it is considered a moderate speeding problem (30-35 mph) or an excessive speeding problem (over 35 mph).

      Here is a graphic display of an 85th percentile example.

      This page was last revised on: December 27, 2003.
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